The present invention broadly relates to semiconductor wafer processing equipment, and deals more particularly with an improved pod employed to protectively enclose and transfer a cassette containing a plurality of semiconductor wafers.
The high level of automation used in fabricating semiconductor devices relies on sophisticated handling and transport equipment for moving semiconductor wafers between various processing stations. Most handling and transport operations are conducted under automatic control using a programmed computer which issues control signals for operating the equipment with little or no intervention by an operator. In many systems, standard mechanical interface (SMIF) pods are used to transport batches of wafers that are stored in cassettes. These pods include a base upon which the cassettes rest, and a cover removably secured to the base and completely enclosing the cassette. The cover protectively surrounds the cassette, and thus the wafers, from the surrounding environment which may contain airborne, contamination particles. SMIF pods are most often used to transport cassettes from one clean room environment to another, where during the transport movement, the wafers, if not covered, are exposed to the contaminating environment.
After a pod has reached the vicinity of a processing station within a protected, clean room environment, it is necessary to remove the cover so that automated wafer transfer robots can gain access the individual wafers held in the cassette. The covers are held on the pods by various types of latching mechanisms which are automatically actuated to latch and unlatch the cover by means of actuating controls positioned at each processing station. Thus, when a pod reaches a processing station, control mechanisms engage the latch mechanism on the pod to unlatch the cover, following which either an operator or a robotic mechanism removes the cover to expose the cassette. Following processing of a batch of wafers in the cassette, the cover is reinstalled on the pod base, either manually or robotically, after which the control mechanism is actuated to latch the cover on the base before the pod leaves the processing station.
In spite of the fact that positive latch mechanisms are employed to lock the cover on the pod base, occasions arise when, for a variety of reasons, the latch fails to lock the cover on the pod base. This may occur, for example, when a foreign article becomes lodged between the cover and the base or where the cassette becomes tilted on the base, thus interfering with proper seating of the cover. In other cases, the control mechanism for actuating the latch may malfunction. In many cases, failure of the latch mechanism to lock the cover on the pod base goes undetected by process operators. As a result, it is possible that contaminants may pass between the pod base and cover when the pod leaves the clean room environment thereby resulting in possible contamination of the wafers.
Accordingly, there is a clear need in the art for an improved pod construction which provides a positive indication of when the cover is properly locked down on the pod base. The present invention is directed toward satisfying this need in the art.
The present invention relates to a pod for transporting a cassette containing a plurality of semiconductor wafers. The pod includes a base for supporting the cassette thereon, and a cover removably carried on the base for protectively covering the cassette. Latch means are carried on the base for latching the cover on the base. The latch means is actuatable from a closed, latched position in which the cover is locked down on the base, to a released, open condition allowing the cover to be removed from the base. Means are provided on the base for providing an operator with a positive, visual indication that the latching means has properly locked down the cover on the base. The indicator means includes an electrical power source, preferably a battery, carried on the base, an indicator light such as an LED, and an electrical switch which is actuated by the latch means. The latch means include a pair of slidably latch members on the base which engage and lock the cover, as well as a rotatable drive member on the base which is powered by a separate control mechanism at a processing station. The drive member preferably comprises a rotatable plate having a pair of drive pins on the outer periphery thereof. The latch members each include a slot therein for receiving a corresponding one of the drive pins. The drive pins translate the rotational motion of the drive member to linear motion, causing the latch members to slide in either of two directions respectively corresponding to an open position in which the cover may be removed from the base, and a closed, locked position in which the cover is secured on the base.
Both the drive member and the latch members are formed of electrically nonconductive material, while the drive pins are electrically conductive. The electrical switches used to switch power to the indicator lights are carried on the latch members and are switched by movement of the drive pins which act as electrical contacts.
It is therefore a primary object of the present invention to provide a semiconductor wafer cassette carrying pod that eliminates the possibility of wafer breakage or damage as the result of the failure of a cover to be properly locked to the pod base.
Another object of the invention is to provide a pod of the type mentioned above in which positive locking of the cover on the pod base is confirmed by an indicator light on the pod.
Another object of the invention is to provide a pod as described above wherein the state of the cover latching mechanism is positively displayed in view of an operator.
A still further object of the invention is to provide a pod as described above in which the indicator employs a latch sensing system that is simple and economical in design, and which may be retrofitted to existing pods.
These, and further objects and advantages of the present invention will be made clear or will become apparent during the course of the following description of a preferred embodiment of the present invention.